WO2023026783A1 - Gas separation system and method for separating mixed gas - Google Patents

Abstract

The present invention provides a gas separation system suitable for efficiently separating a mixed gas. The gas separation system 100 according to the present invention comprises a first separation membrane 11 that separates a mixed gas 70 into a first permeating gas 80 and a first non-permeating gas 81, and a second separation membrane 21 that separates the first non-permeating gas 81 into a second permeating gas 90 and a second non-permeating gas 91. The mixed gas 70 includes a gas A and a gas B different from the gas A. The first separation membrane 11 preferentially allows the gas A to pass therethrough. The second separation membrane 21 preferentially allows the gas B to pass therethrough. The membrane area of the first separation membrane 11 is smaller than the membrane area of the second separation membrane 21. In the gas separation system 100, the second permeating gas 90 and the second non-permeating gas 91 are separately collected.

Description

Gas separation system and method for separating mixed gas

The present invention relates to a gas separation system and a mixed gas separation method.

At chemical plants that manufacture chemicals, for example, mixed gases containing carbon dioxide and hydrogen are emitted. From the viewpoint of environmental regulations and effective use of resources, it is desirable to separate and recover each component of the mixed gas.

A membrane separation method has been developed as a method for separating each component from a mixed gas. The membrane separation method can efficiently separate each component while suppressing the operating cost, compared to the absorption method in which specific components contained in the mixed gas are separated by being absorbed by an absorbent.

In the membrane separation method, a gas separation system that combines multiple separation membranes is sometimes used. For example, Patent Literature 1 discloses a gas production system provided with a carbon dioxide separation membrane and a hydrogen separation membrane. Patent Document 1 describes that a generated gas containing hydrogen and carbon dioxide is treated with a carbon dioxide separation membrane, and non-permeated gas that has not permeated the carbon dioxide separation membrane is further treated with a hydrogen separation membrane. In the gas production system of Patent Document 1, carbon dioxide permeated through the carbon dioxide separation membrane and hydrogen permeated through the hydrogen separation membrane are recovered as product gases.

JP 2018-162184 A

In the conventional gas separation system, in order to improve the recovery rate of each component separated from the mixed gas, it is necessary to greatly increase the membrane area of the separation membrane provided in the gas separation system. However, when the membrane area of the separation membrane increases, not only does the production cost of the separation membrane increase, but the content (purity) of the target component in the permeated gas that has passed through the separation membrane tends to decrease.

Therefore, an object of the present invention is to provide a gas separation system suitable for efficiently separating a mixed gas.

The present invention
a first separation membrane that separates the mixed gas into a first permeable gas and a first non-permeable gas;
a second separation membrane that separates the first non-permeable gas into a second non-permeable gas and a second non-permeable gas;
with
The mixed gas includes a gas A and a gas B different from the gas A,
The first separation membrane can preferentially permeate the gas A,
The second separation membrane can preferentially permeate the gas B,
the membrane area of the first separation membrane is smaller than the membrane area of the second separation membrane,
A gas separation system is provided for recovering the second permeate gas and the second non-permeate gas, respectively.

Furthermore, the present invention
A mixed gas containing the gas A and a gas B different from the gas A is separated into a first permeable gas and a first non-permeable gas by a first separation membrane capable of preferentially permeating the gas A. a first separation step;
a second separation step of separating the first non-permeable gas into a second non-permeable gas and a second non-permeable gas by a second separation membrane capable of preferentially permeating the gas B;
a recovery step of recovering the second permeable gas and the second non-permeable gas, respectively;
including
A mixed gas separation method is provided in which the membrane area of the first separation membrane is smaller than the membrane area of the second separation membrane.

According to the present invention, it is possible to provide a gas separation system suitable for efficiently separating a mixed gas.

1 is a schematic configuration diagram of a gas separation system according to one embodiment of the present invention; FIG. 1 is a schematic cross-sectional view showing an example of a first separation membrane unit; FIG. FIG. 4 is a cross-sectional view showing an example of a first separation membrane; FIG. 4 is a cross-sectional view showing another example of the first separation membrane; FIG. 4 is a schematic cross-sectional view showing an example of a second separation membrane unit; FIG. 4 is a schematic cross-sectional view showing another example of the first separation membrane unit; FIG. 2 is a configuration diagram for explaining the gas separation systems of Models 2 and 5; FIG. 2 is a configuration diagram for explaining a gas separation system of model 4;

The gas separation system according to the first aspect of the present invention comprises
a first separation membrane that separates the mixed gas into a first permeable gas and a first non-permeable gas;
a second separation membrane that separates the first non-permeable gas into a second non-permeable gas and a second non-permeable gas;
with
The mixed gas includes a gas A and a gas B different from the gas A,
The first separation membrane can preferentially permeate the gas A,
The second separation membrane can preferentially permeate the gas B,
the membrane area of the first separation membrane is smaller than the membrane area of the second separation membrane,
The second permeable gas and the second non-permeable gas are each recovered.

In the second aspect of the present invention, for example, in the gas separation system according to the first aspect, the ratio of the membrane area of the first separation membrane to the membrane area of the second separation membrane is 10/90 or less.

In a third aspect of the present invention, for example, in the gas separation system according to the first or second aspect, (i) said gas A is hydrogen and said gas B is carbon dioxide, or (ii) said gas A is carbon dioxide and said gas B is hydrogen.

In the fourth aspect of the present invention, for example, in the gas separation system according to any one of the first to third aspects, the content of the gas B in the second permeating gas is 70 vol% or more, and the second The content of the gas A in the impermeable gas is 70 vol % or more.

In the fifth aspect of the present invention, for example, in the gas separation system according to any one of the first to fourth aspects, the recovery rate of the gas B by the second permeating gas is 70% or more, and the second The recovery rate of the gas A by the non-permeating gas is 60% or more.

In the sixth aspect of the present invention, for example, in the gas separation system according to any one of the first to fifth aspects, in the mixed gas, for the total value of the volume of the gas A and the volume of the gas B, The volume ratio of the gas A is 25-75 vol %.

In a seventh aspect of the present invention, for example, the gas separation system according to any one of the first to sixth aspects includes a first separation membrane unit containing the first separation membrane, and It further comprises a mixed gas supply path connected to supply the mixed gas to the first separation membrane unit, and a pressurizing device arranged in the mixed gas supply path for pressurizing the mixed gas.

In the eighth aspect of the present invention, for example, the gas separation system according to any one of the first to seventh aspects includes a second separation membrane unit containing the second separation membrane, and recovering the second permeated gas and a first recovery path connected to the second separation membrane unit and the first recovery section for sending the second permeated gas to the first recovery section.

In the ninth aspect of the present invention, for example, the gas separation system according to any one of the first to eighth aspects includes a second separation membrane unit containing the second separation membrane, and a second non-permeable gas. It further comprises a second recovery section for recovery, and a second recovery path connected to the second separation membrane unit and the second recovery section for sending the second non-permeating gas to the second recovery section.

In the tenth aspect of the present invention, for example, in the gas separation system according to any one of the first to ninth aspects, one of the first separation membrane and the second separation membrane is a metal layer containing a metal It has

In the eleventh aspect of the present invention, for example, in the gas separation system according to any one of the first to tenth aspects, one of the first separation membrane and the second separation membrane is a polyether block amide resin Alternatively, it has a separation function layer containing an ionic liquid.

The mixed gas separation method according to the twelfth aspect of the present invention includes:
A mixed gas containing the gas A and a gas B different from the gas A is separated into a first permeable gas and a first non-permeable gas by a first separation membrane capable of preferentially permeating the gas A. a first separation step;
a second separation step of separating the first non-permeable gas into a second non-permeable gas and a second non-permeable gas by a second separation membrane capable of preferentially permeating the gas B;
a recovery step of recovering the second permeable gas and the second non-permeable gas, respectively;
including
The membrane area of the first separation membrane is smaller than the membrane area of the second separation membrane.

Although the details of the present invention will be described below, the following description is not intended to limit the present invention to specific embodiments.

<Gas separation system>
As shown in FIG. 1 , the gas separation system 100 of this embodiment includes a first separation membrane 11 and a second separation membrane 21 . Specifically, the gas separation system 100 includes a first separation membrane unit 10 containing a first separation membrane 11 and a second separation membrane unit 20 containing a second separation membrane 21 . The first separation membrane unit 10 is a membrane separation device that uses the first separation membrane 11 to perform membrane separation on a mixed gas. The first separation membrane 11 can separate the mixed gas into a first permeable gas and a first non-permeable gas. The second separation membrane unit 20 is a membrane separation device that uses the second separation membrane 21 to perform membrane separation on the first non-permeating gas discharged from the first separation membrane unit 10 . The second separation membrane 21 can separate the first non-permeable gas into a second non-permeable gas and a second non-permeable gas.

The mixed gas processed by the first separation membrane unit 10 contains gas A and gas B different from gas A. Examples of gas A and gas B include hydrogen and carbon dioxide. As an example, (i) gas A is hydrogen and gas B is carbon dioxide, or (ii) gas A is carbon dioxide and gas B is hydrogen.

The first separation membrane 11 can preferentially permeate the gas A. Therefore, the first permeable gas separated by the first separation membrane 11 has a higher content of gas A than the mixed gas and a lower content of gas B than the mixed gas. On the other hand, the first impermeable gas has a lower content of gas A than the mixed gas and a higher content of gas B than the mixed gas.

The second separation membrane 21 can preferentially permeate the gas B. Therefore, the second permeable gas separated by the second separation membrane 21 has a higher content of gas B than the first non-permeable gas and a lower content of gas A than the first non-permeable gas. On the other hand, the second non-permeable gas has a lower gas B content than the first non-permeable gas and a higher gas A content than the first non-permeable gas.

In the gas separation system 100, the membrane area M1 of the first separation membrane 11 is smaller than the membrane area M2 of the second separation membrane 21. According to the configuration of the gas separation system 100, the sum of the membrane area M1 of the first separation membrane 11 and the membrane area M2 of the second separation membrane 21 is It tends to be possible to recover each of Gas A and Gas B with high purity and high recovery without a significant increase in value. Thus, the gas separation system 100 of this embodiment is suitable for efficiently separating a mixed gas.

The ratio M1/M2 of the membrane area M1 of the first separation membrane 11 to the membrane area M2 of the second separation membrane 21 is, for example, 40/60 or less, preferably 25/75 or less, and more preferably 10/90 or less. and may be 8/92 or less, or may be 5/95 or less. The lower limit of the ratio M1/M2 is not particularly limited, and is, for example, 0.5/99.5.

The gas separation system 100 further includes a mixed gas supply route 30. The mixed gas supply path 30 is connected to the mixed gas inlet (inlet 13a) of the first separation membrane unit 10, and the mixed gas is mixed into the first separation membrane unit 10 from a tank (not shown) storing the mixed gas. It is a path for supplying gas. The mixed gas supply path 30 may be directly connected to the source of the mixed gas, or may be configured to continuously supply the mixed gas from the source to the first separation membrane unit 10 . For example, a pressure device 40 that pressurizes the mixed gas is arranged in the mixed gas supply path 30 . The pressurization device 40 includes, for example, a compressor, a blower and a back pressure valve. The pressurizing device 40 can pressurize the supply-side space of the first separation membrane unit 10 by pressurizing the mixed gas.

A heat exchanger (not shown) may be arranged between the pressurizing device 40 and the first separation membrane unit 10 in the mixed gas supply path 30 . The heat exchanger cools the mixed gas pressurized by the pressurizing device 40, for example. The heat exchanger is, for example, a gas-liquid heat exchanger that causes heat exchange between a cooling medium such as antifreeze and a mixed gas, typically a fin-tube heat exchanger.

The gas separation system 100 further comprises a non-permeable gas supply path 32 . The non-permeating gas supply path 32 is connected to the non-permeating gas outlet (outlet 13b) of the first separation membrane unit 10 and the non-permeating gas inlet (inlet 23a) of the second separation membrane unit 20, This path is for supplying the first non-permeating gas to the second separation membrane unit 20 . The impermeable gas supply path 32 may not be provided with a tank such as a collector that collects the first impermeable gas or an on-off valve that opens and closes the path. According to such a configuration, the first non-permeating gas discharged from the first separation membrane unit 10 can be continuously supplied to the second separation membrane unit 20, and the mixed gas processing amount per unit time can be reduced to can be easily increased. As an example, the non-permeating gas supply path 32 may be composed only of piping.

The gas separation system 100 further comprises an exhaust path 34 . The discharge path 34 is connected to the permeated gas outlet (outlet 14 a ) of the first separation membrane unit 10 and is a path for discharging the first permeated gas from the first separation membrane unit 10 . An opening (discharge port 42 ) for discharging the first permeating gas from the discharge path 34 is formed in the discharge path 34 . Gas separation system 100, for example, discards the first permeate gas without recovery. However, the discharge path 34 may be connected to a second recovery section 46 to be described later, and the first permeation gas may be recovered in the second recovery section 46 . A discharge path 34 is connected to the mixed gas supply path 30, and the first permeate gas may be reused.

The gas separation system 100 further includes a first recovery path 36 and a first recovery section 44 . The first recovery path 36 is connected to the permeated gas outlet (outlet 24a) of the second separation membrane unit 20 and the inlet of the first recovery section 44, and the second It is the path for sending the permeating gas. The first collection section 44 can collect the second permeation gas sent from the second separation membrane unit 20 and store the second permeation gas, for example. The 1st collection|recovery part 44 is a tank which stores a 2nd permeation|transmission gas, for example.

The gas separation system 100 further includes a second recovery path 38 and a second recovery section 46 . The second recovery path 38 is connected to the non-permeating gas outlet (outlet 23b) of the second separation membrane unit 20 and the inlet of the second recovery section 46, and the second recovery section 46 from the second separation membrane unit 20 2 path for sending non-permeating gas. The second collection section 46 can collect the second non-permeable gas sent from the second separation membrane unit 20 and store the second non-permeable gas, for example. The second recovery section 46 is, for example, a tank that stores the second non-permeable gas.

A decompression device and a heat exchanger (not shown) may be arranged in the second recovery path 38 . For example, the pressure reducing device can reduce the pressure of the second non-permeating gas to the atmospheric pressure (for example, 101 kPa) in the external environment. Examples of the decompression device include a decompression valve. The heat exchanger is located, for example, between the decompression device and the second recovery section 46 . A heat exchanger heats the 2nd non-permeate gas pressure-reduced by the pressure reduction apparatus, for example. The heat exchanger is, for example, a gas-liquid heat exchanger that causes heat exchange between a heat medium such as hot water and a second non-permeable gas, typically a finned-tube heat exchanger.

Unless otherwise specified, each path of the gas separation system 100 is composed of, for example, metal or resin piping.

The gas separation system 100 may further include a controller (not shown) that controls each component of the gas separation system 100 . The controller is, for example, a DSP (Digital Signal Processor) including an A/D conversion circuit, an input/output circuit, an arithmetic circuit, a storage device, and the like. The controller stores a program for proper operation of the gas separation system 100 .

The gas separation system 100 of this embodiment is, for example, a continuous system. In the present specification, a continuous system means a system capable of continuously processing a mixed gas without closing a path that constitutes the gas separation system 100 with an on-off valve or the like. In other words, the gas separation system 100 treats the mixed gas in the first separation membrane unit 10, and the first non-permeating gas obtained in the first separation membrane unit 10 is immediately It can be processed in the second separation membrane unit 20 . Thus, the gas separation system 100 of this embodiment is capable of continuous operation. The gas separation system 100, functioning as a continuous system, is suitable for applications where mixed gases are continuously supplied, exhaust gas treatment, and the like.

[First separation membrane unit]
As shown in FIG. 2 , the first separation membrane unit 10 includes a first separation membrane 11 and a tank 12 . Tank 12 has a first chamber 13 and a second chamber 14 . The space within the first chamber 13 corresponds to the supply side space, and the space within the second chamber 14 corresponds to the permeation side space. The first separation membrane 11 is arranged inside the tank 12 . Inside the tank 12 , the first separation membrane 11 separates the first chamber 13 and the second chamber 14 . The first separation membrane 11 extends from one of the pair of wall surfaces of the tank 12 to the other.

The first chamber 13 has an entrance 13a and an exit 13b. The second chamber 14 has an outlet 14a. The inlet 13 a of the first chamber 13 is an opening for supplying the mixed gas 70 to the first separation membrane unit 10 . The outlet 14 a of the second chamber 14 is an opening for discharging the first permeated gas 80 obtained by permeating the mixed gas 70 through the first separation membrane 11 from the first separation membrane unit 10 . The outlet 13 b of the first chamber 13 is an opening for discharging the mixed gas 70 (first non-permeating gas 81 ) that has not permeated the first separation membrane 11 from the first separation membrane unit 10 . Each of the inlet 13a, the outlet 13b, and the outlet 14a is formed in the wall surface of the tank 12, for example.

(First separation membrane)
The first separation membrane 11 can preferentially permeate the gas A contained in the mixed gas 70 . Below, the first separation membrane 11 when the gas A is hydrogen, that is, the first separation membrane 11 that preferentially allows hydrogen to permeate will be described. In this specification, a separation membrane that preferentially permeates hydrogen may be referred to as a "hydrogen permeable membrane".

As shown in FIG. 3A, the first separation membrane 11 as a hydrogen-permeable membrane has, for example, a metal layer 1 containing metal. The first separation membrane 11 may further include a support 3 that supports the metal layer 1 and a coat layer 2 that covers the metal layer 1 . The metal layer 1 is arranged, for example, between the coat layer 2 and the support 3 and is in direct contact with the coat layer 2 and the support 3 respectively. However, an adhesive may be arranged between the metal layer 1 and the support 3 . Another support may be further arranged between the metal layer 1 and the coat layer 2 .

≪Metal layer≫
The metal layer 1 is a layer that allows preferential transmission of hydrogen. The metal contained in the metal layer 1 is not particularly limited as long as it has a hydrogen permeation function by itself or by being alloyed. Examples of such metals include Pd, Nb, V, Ta, Ni, Fe, Al, Cu, Ru, Re, Rh, Au, Pt, Ag, Cr, Co, Sn, Zr, Y, Ce, Ti , Ir, Mo, and alloys containing two or more of these metals.

The metal layer 1 is preferably an alloy layer containing a Pd alloy. Other metals forming the Pd alloy are not particularly limited, but are preferably Group 11 elements, more preferably at least one selected from the group consisting of Au, Ag and Cu. Metal layer 1 preferably contains a Pd—Au alloy. The content of Group 11 elements in the Pd alloy is preferably 20 to 65 mol%, more preferably 30 to 65 mol%, still more preferably 30 to 60 mol%, and particularly preferably 40 to 60 mol%. . An alloy layer containing a Pd—Ag alloy with an Ag content of 20 mol% or more, a Pd—Cu alloy with a Cu content of 30 mol% or more, or a Pd—Au alloy with an Au content of 20 mol% or more , even in a low temperature range of about 60° C. or less, it tends to be difficult to become embrittled by hydrogen. The Pd alloy may contain Group IB and/or Group IIIA metals.

The Pd alloy may be an alloy of three or more components instead of the two-component alloy described above. Examples of alloys of three or more components include Pd--Au--Ag, Pd--Au--Cu and Pd--Au--Ag--Cu. For example, in the case of a multi-component alloy containing Pd, Au and other metals, the total content of Au and other metals in the alloy is preferably 55 mol% or less, more preferably 50 mol. %, more preferably 45 mol % or less, and particularly preferably 40 mol % or less.

The metal layer 1 is, for example, substantially made of metal. As used herein, "consisting essentially of" means excluding other ingredients that alter the essential characteristics of the material referred to, such as 95 wt% or more, or even 99 wt% or more of the material. It means that it is composed of

The metal layer 1 can be produced by, for example, a rolling method, a sputtering method, a vacuum deposition method, an ion plating method, a plating method, or the like. The rolling method is suitable for producing relatively thick metal layers 1 . Sputtering methods are suitable for producing relatively thin metal layers 1 .

The rolling method may be hot rolling or cold rolling. The rolling method is a method in which a pair or a plurality of pairs of rolls are used to apply pressure to a metal while stretching it into a film. The thickness of the metal layer 1 obtained by rolling is preferably 5 to 50 μm, more preferably 10 to 30 μm. By setting the thickness of the metal layer 1 to 5 μm or more, it is possible to suppress the occurrence of pinholes or cracks during fabrication, and further to suppress deformation when hydrogen is absorbed. By setting the thickness of the metal layer 1 to 50 μm or less, the metal layer 1 can achieve sufficient hydrogen permeability while suppressing manufacturing costs.

The sputtering method can be performed by the following method using a parallel plate type, single wafer type, passing type, DC sputtering, RF sputtering, or other sputtering apparatus. First, a substrate is attached to a sputtering apparatus in which a metal target is set. Next, the inside of the sputtering apparatus is evacuated, and the Ar gas pressure is adjusted to a predetermined value. A predetermined sputtering current is passed through the metal target to form a metal film on the substrate. The metal layer 1 can be obtained by peeling the metal film from the substrate. As the metal target, one or two or more targets can be used depending on the composition of the metal layer 1 to be produced. Substrates used in the sputtering method include, for example, glass plates, ceramic plates, silicon wafers, and metal plates containing aluminum, stainless steel, and the like. The metal layer 1 can also be directly formed on the support 3 by sputtering.

The thickness of the metal layer 1 obtained by sputtering is preferably 0.01 to 5 μm, more preferably 0.05 to 2 μm. By setting the thickness of the metal layer 1 to 0.01 μm or more, it is possible to suppress the occurrence of pinholes during fabrication and to obtain sufficient mechanical strength. If the thickness of the metal layer 1 is 0.01 μm or more, it tends to be less likely to be damaged when peeled off from the substrate and easy to handle after peeling. When the thickness of the metal layer 1 is 5 μm or less, the metal layer 1 can be produced in a short time, and the manufacturing cost can be suppressed.

≪Coating layer≫
The material of the coat layer 2 is not particularly limited, and examples thereof include fluorine-based compounds, rubber-based polymers, silicone-based polymers, urethane-based polymers, and polyester-based polymers. At least one selected from the group consisting of polymers is preferred.

Examples of fluorine compounds include fluoroalkyl group-containing compounds such as fluoroalkyl carboxylates, fluoroalkyl quaternary ammonium salts, and fluoroalkyl ethylene oxide adducts; perfluoroalkyl carboxylates, perfluoroalkyl quaternary ammonium salts, perfluoro Perfluoroalkyl group-containing compounds such as alkylethylene oxide adducts; tetrafluoroethylene/hexafluoropropylene copolymer, tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene polymer, vinylidene fluoride/tetrafluoroethylene copolymer Coalescence, vinylidene fluoride/hexafluoropropylene copolymer, fluorine-containing (meth)acrylic acid ester polymer, fluorine-containing (meth)acrylic acid alkyl ester polymer, copolymerization of fluorine-containing (meth)acrylic acid ester and other monomers fluorine-based polymers such as coalescence; fluorine-containing (meth)acrylic acid esters; As the fluorine-based compound, the “Durasurf” series manufactured by Harves, the “Optool” series manufactured by Daikin Industries, the “KY-100” series manufactured by Shin-Etsu Chemical Co., Ltd., and the like may be used.

Examples of rubber-based polymers include natural rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, chloroprene rubber, polyisoprene rubber, polybutadiene rubber, ethylene-propylene rubber, ethylene-propylene-diene terpolymer rubber, chlorosulfonated polyethylene rubber, Examples include ethylene-vinyl acetate copolymer rubber. As the rubber-based polymer, the "ELEPCOAT" series manufactured by Nitto Shinko Co., Ltd. may be used.

Examples of silicone-based polymers include polydimethylsiloxane, alkyl-modified polydimethylsiloxane, carboxyl-modified polydimethylsiloxane, amino-modified polydimethylsiloxane, epoxy-modified polydimethylsiloxane, fluorine-modified polydimethylsiloxane, and (meth)acrylate-modified polydimethylsiloxane. etc.

The coat layer 2 can be formed, for example, by applying a composition containing the material of the coat layer 2 onto the metal layer 1 and curing the composition. The method of applying the composition is not particularly limited, and examples thereof include roll coating, spin coating, dip coating, spray coating, bar coating, knife coating, die coating, inkjet, and gravure coating. be done.

The solvent contained in the composition can be appropriately selected according to the raw material of the coat layer 2. When a fluorine-based compound is used as the material of the coat layer 2, one or a mixture of two or more of fluorine-based solvents, alcohol-based solvents, ether-based solvents, ester-based solvents, hydrocarbon-based solvents, etc. is used as a solvent. be able to. Among these solvents, it is preferable to use a non-flammable and rapidly volatilizing fluorine-based solvent alone or in combination with another solvent.

Examples of fluorine-based solvents include hydrofluoroethers, perfluoropolyethers, perfluoroalkanes, hydrofluoropolyethers, hydrofluorocarbons, perfluorocycloethers, perfluorocycloalkanes, hydrofluorocycloalkanes, xylene hexafluoride, hydro Examples include fluorochlorocarbons and perfluorocarbons.

The thickness of the coat layer 2 is not particularly limited, but is preferably 0.1 μm or more, more preferably 0.3 μm or more, still more preferably 0.5 μm or more, and particularly preferably 1.0 μm or more. be. The thickness of the coating layer 2 is, for example, 80 µm or less, preferably 50 µm or less, more preferably 30 µm or less, still more preferably 20 µm or less, particularly preferably 10 µm or less, and particularly preferably 5 µm or less. is. The thickness of the coat layer 2 can be adjusted by the solid content concentration of the composition containing the material of the coat layer 2 and the number of times the composition is applied. Coat layer 2 is preferably non-porous.

<<Support>>
The support 3 is not particularly limited as long as it has hydrogen permeability and supports the metal layer 1, and is, for example, a porous body. However, the support 3 may be imperforate. The support 3 may be a woven fabric, a non-woven fabric, or the like. Materials for the support 3 include polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polyethylene naphthalate; polyarylethersulfones such as polysulfone and polyethersulfone; fluorine resins such as polytetrafluoroethylene and polyvinylidene fluoride; Epoxy resin; polyamide; polyimide, etc., and polysulfone or polytetrafluoroethylene, which are chemically and thermally stable, are preferred.

The support 3 is preferably a porous body with an average pore size of 100 μm or less. Since this porous body has sufficient surface smoothness, the metal layer 1 having a uniform thickness can be easily formed when the metal layer 1 is directly formed on the porous body by a sputtering method or the like. At this time, the occurrence of pinholes or cracks in the metal layer 1 can also be suppressed. The thickness of the support 3 is not particularly limited, and is, for example, 5-1000 μm, preferably 10-300 μm.

<<Characteristics of the first separation membrane>>
The permeation rate of hydrogen permeating through the first separation membrane 11 is not particularly limited. As an example, the permeation rate T _H2 of hydrogen permeating the first separation membrane 11 is, for example, 5 GPU or more, preferably 10 GPU or more, more preferably 50 GPU or more, and still more preferably 100 GPU or more. The upper limit of the transmission speed T _H2 is not particularly limited, and is, for example, 500 GPU. However, GPU means 10 ⁻⁶ ·cm ³ (STP)/(sec·cm ² ·cmHg). cm ³ (STP) means the volume of gas at 1 atmosphere and 0°C.

The permeation rate T _H2 can be calculated by the following method. First, a mixed gas containing carbon dioxide and hydrogen is supplied to a space adjacent to one surface of the first separation membrane 11 (for example, the main surface 11a of the first separation membrane 11 on the coat layer side), and the first separation membrane 11 (eg, main surface 11b of first separation membrane 11 on the support side) is decompressed. Thereby, in the space adjacent to the other surface of the first separation membrane 11, the permeated gas that has passed through the first separation membrane 11 is obtained. The composition of the permeated gas, the weight of the permeated gas, etc. are measured. The permeation rate T _H2 can be calculated from the measurement results. In the above operation, the concentration of hydrogen in the mixed gas is 50 vol % under standard conditions (0° C., 101 kPa). The mixed gas supplied to the space adjacent to one surface of the first separation membrane 11 has a temperature of 30° C. and a pressure of 0.1 MPa. The space adjacent to the other surface of the first separation membrane 11 is decompressed so that the pressure in the space is 0.1 MPa lower than the atmospheric pressure in the measurement environment.

Under the conditions for measuring the permeation rate T _H2 , the separation coefficient α _H2 of hydrogen with respect to carbon dioxide of the first separation membrane 11 is, for example, 20 or more, preferably 30 or more, more preferably 40 or more, and further Preferably it is 50 or more. The upper limit of the separation factor α _H2 is not particularly limited, and is 100, for example. The separation factor α _H2 can be calculated from the following formula. However, in the following formula, X _A and X _B are the volume ratio of hydrogen and the volume ratio of carbon dioxide in the mixed gas, respectively. Y _A and Y _B are the volume ratio of hydrogen and the volume ratio of carbon dioxide in the permeated gas that has permeated the first separation membrane 11, respectively.
Separation factor α _H2 = (Y _A /Y _B )/(X _A /X _B )

(Modified example of the first separation membrane)
The first separation membrane 11 is not limited to the above hydrogen permeable membrane. Below, the first separation membrane 11 when the gas A is carbon dioxide, that is, the first separation membrane 11 that preferentially permeates carbon dioxide will be described. In this specification, a separation membrane that preferentially permeates carbon dioxide may be referred to as a "carbon dioxide permeable membrane".

As shown in FIG. 3B, the first separation membrane 11 as a carbon dioxide permeation membrane has a separation function layer 5, for example. The first separation membrane 11 may further comprise a porous support 7 supporting the separation functional layer 5 and an intermediate layer 6 arranged between the separation functional layer 5 and the porous support 7. . The intermediate layer 6 is in direct contact with the separation functional layer 5 and the porous support 7, for example.

≪Separation function layer≫
The separation functional layer 5 is a layer that allows carbon dioxide to preferentially permeate. In one preferred form, the separation functional layer 5 contains a resin. Examples of resins contained in the separation functional layer 5 include polyether block amide resins, polyamide resins, polyether resins, polyimide resins, cellulose acetate resins, silicone resins, and fluorine resins. The separation functional layer 5 preferably contains a polyether block amide resin. In this form, the separation functional layer 5 is preferably substantially made of resin.

In another preferred form, the separation functional layer 5 contains an ionic liquid. An ionic liquid is a salt (ionic compound) that is liquid at 25°C. The separation functional layer 5 has, for example, a double network gel containing an ionic liquid. A double network gel is a gel that has two types of network structures that are independent of each other. A double network gel includes, for example, a first network structure mainly composed of an organic material, a second network structure mainly composed of an inorganic material, and an ionic liquid. As used herein, "mainly composed of" means that 50 wt% or more, or even 70 wt% or more is composed of the material.

The organic material for forming the first network structure includes, for example, a polymer such as polyacrylamide (especially polydialkylacrylamide such as polydimethylacrylamide). The polymer contained in the organic material has a structural unit derived from an acrylamide derivative and may further contain a crosslinked structure. A polymer containing a crosslinked structure can be produced by a known method. For example, first, a prepolymer having structural units having N-hydroxysuccinimide ester groups is prepared. A structural unit having an N-hydroxysuccinimide ester group is derived from, for example, N-acryloxysuccinimide. Next, a polymer containing a crosslinked structure can be obtained by reacting the prepolymer with an amine-based crosslinking agent. Amine crosslinkers are compounds with two or more primary amino groups, such as ethylene glycol bis(3-aminopropyl) ether.

The second network structure may include a network of multiple particles. A network of a plurality of particles is formed, for example, by bonding a plurality of particles to each other through hydrogen bonding. Particles included in the second network structure may be particles exemplified as nanoparticles to be described later. As an example, the particles included in the second network structure are silica particles.

In the present embodiment, specific ionic liquids include, for example, ionic liquids having imidazolium, pyridinium, ammonium, or phosphonium and substituents having 1 or more carbon atoms.

In the ionic liquid containing imidazolium and a substituent having 1 or more carbon atoms, the substituent having 1 or more carbon atoms includes an alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 14 carbon atoms, and a cycloalkyl group having 3 to 14 carbon atoms. 6 or more and 20 or less aryl groups, etc., which may be further substituted with a hydroxy group, a cyano group, an amino group, a monovalent ether group or the like (for example, a hydroxyalkyl group having 1 or more and 20 or less carbon atoms etc).

Examples of alkyl groups having 1 to 20 carbon atoms include methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n- nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n- nonadecyl group, n-eicosadecyl group, i-propyl group, sec-butyl group, i-butyl group, 1-methylbutyl group, 1-ethylpropyl group, 2-methylbutyl group, i-pentyl group, neopentyl group, 1,2 -dimethylpropyl group, 1,1-dimethylpropyl group, t-pentyl group, 2-ethylhexyl group, 1,5-dimethylhexyl group and the like, which further include hydroxy group, cyano group, amino group, monovalent It may be substituted with an ether group or the like.

The above alkyl group may be substituted with a cycloalkyl group. The number of carbon atoms in the alkyl group substituted by the cycloalkyl group is, for example, 1 or more and 20 or less. Alkyl groups substituted by cycloalkyl groups include cyclopropylmethyl, cyclobutylmethyl, cyclohexylmethyl, cyclohexylpropyl groups and the like, which further include hydroxy, cyano, amino, monovalent ether It may be substituted with a group or the like.

Examples of cycloalkyl groups having 3 to 14 carbon atoms include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclododecyl, norbornyl, bornyl and adamantyl groups. , and these may be further substituted with a hydroxy group, a cyano group, an amino group, a monovalent ether group, or the like.

Examples of the aryl group having 6 to 20 carbon atoms include phenyl, toluyl, xylyl, mesityl, anisyl, naphthyl, benzyl, etc. These are further hydroxy, cyano, amino, mono may be substituted with a valent ether group or the like.

The compound having imidazolium and a substituent having 1 or more carbon atoms may further have a substituent such as an alkyl group, and may form a salt with a counter anion. Counter anions include alkylsulfate, tosylate, methanesulfonate, acetate, bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, thiocyanate, dicyanamide, tricyanometanide, tetracyanoborate, hexafluorophosphate, tetrafluoro Examples include borates and halides, and bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, dicyanamide, tricyanometanide, and tetracyanoborate are preferred from the viewpoint of gas separation performance.

Specific examples of ionic liquids having imidazolium and substituents having 1 or more carbon atoms include 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide and 1-ethyl-3-methylimidazolium dicyanamide. , 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1 -butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium tetrachloroferrate, 1-butyl-3-methylimidazolium iodide, 1-butyl-2,3-dimethylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium hexafluorophosphate, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1 -butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium trifluoro(trifluoromethyl)borate, 1-butyl-3-methylimidazolium tribromide, 1, 3-dimesitylimidazolium chloride, 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride, 1,3-diisopropylimidazolium tetrafluoroborate, 1,3-di-tert-butylimidazolium tetrafluoro Borate, 1,3-dicyclohexylimidazolium tetrafluoroborate, 1,3-dicyclohexylimidazolium chloride, 1,2-dimethyl-3-propylimidazolium iodide, 1-hexyl-3-methylimidazolium chloride, 1-hexyl -3-methylimidazolium hexafluorophosphate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium bromide, 1-methyl-3-propylimidazolium iodide, 1-methyl- 3-n-octylimidazolium bromide, 1-methyl-3-n-octylimidazolium chloride, 1-methyl-3-n-octylimidazolium hexafluorophosphate, 1-methyl-3-[6-(methylsulfinyl) hexyl]imida zolium p-toluenesulfonate, 1-ethyl-3-methylimidazolium tricyanometanide, 1-ethyl-3-methylimidazolium tetracyanoborate, 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoro and romethanesulfonyl)imide.

Among them, from the viewpoint of gas separation performance, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([EMI] [FSI]), 1-ethyl-3-methylimidazolium dicyanamide ([EMI] [DCA]), 1-ethyl-3-methylimidazolium tricyanometanide ([EMI][TCM]), 1-ethyl-3-methylimidazolium tetracyanoborate ([EMI][TCB]), 1- butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C ₄ mim][TF ₂ N]), 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([ _C2OHim ][ _TF2N ]) is particularly preferred.

The method for producing a double network gel is not particularly limited, and for example, the method disclosed in E.Kamio et al., Adv.Mater, 29, 1704118 (2017) can be used.

The content of the ionic liquid in the double network gel is, for example, 50 wt% or more, preferably 60 wt% or more, more preferably 70 wt% or more, and still more preferably 80 wt% or more. The higher the content of the ionic liquid, the more preferentially the separation functional layer 5 can permeate carbon dioxide contained in the mixed gas. The upper limit of the content of the ionic liquid is not particularly limited, and is, for example, 95 wt%.

The content of the first network structure mainly composed of an organic material in the double network gel is, for example, 1 wt% or more, preferably 5 wt% or more, and more preferably 10 wt% or more. The upper limit of the content of the first network structure is, for example, 15 wt%. The content of the second network structure mainly composed of an inorganic material in the double network gel is, for example, 1 wt % or more from the viewpoint of improving the strength of the double network gel. The upper limit of the content of the second network structure is, for example, 5 wt%. The ratio of the sum of the weight of the first network structure and the weight of the second network structure to the weight of the double network gel is, for example, 2 wt% or more, preferably 5 wt% or more, and more preferably 10 wt% or more. . This proportion is preferably less than or equal to 20 wt%. In this form, the separation functional layer 5 preferably consists essentially of a double network gel.

The thickness of the separation functional layer 5 is, for example, 50 μm or less, preferably 25 μm or less, more preferably 15 μm or less. The thickness of the separation function layer 5 may be 10 μm or less, 5.0 μm or less, or 2.0 μm or less depending on the case. The thickness of the separation functional layer 5 may be 0.05 μm or more, or may be 0.1 μm or more.

≪Middle layer≫
The intermediate layer 6 contains, for example, a resin, and may further contain nanoparticles dispersed in the resin (matrix). The nanoparticles may be spaced apart from each other within the matrix or may be partially aggregated. The material of the matrix is not particularly limited, and examples thereof include silicone resins such as polydimethylsiloxane; fluorine resins such as polytetrafluoroethylene; epoxy resins such as polyethylene oxide; polyimide resins; polyacetylene resins such as; and polyolefin resins such as polymethylpentene. The matrix preferably contains a silicone resin.

The nanoparticles may contain inorganic materials or organic materials. Inorganic materials included in nanoparticles include, for example, silica, titania, and alumina. The nanoparticles preferably contain silica.

The thickness of the intermediate layer 6 is not particularly limited, and is, for example, less than 50 μm, preferably 40 μm or less, more preferably 30 μm or less. The lower limit of the thickness of the intermediate layer 6 is not particularly limited, and is, for example, 1 μm. The intermediate layer 6 is, for example, a layer having a thickness of less than 50 μm.

<<Porous support>>
The porous support 7 supports the separation functional layer 5 with the intermediate layer 6 interposed therebetween. Porous support 7 includes, for example, nonwoven fabric; porous polytetrafluoroethylene; aromatic polyamide fiber; porous metal; sintered metal; porous ceramic; silicone; silicone rubber; permeation containing at least one selected from the group consisting of polyvinyl fluoride, polyvinylidene fluoride, polyurethane, polypropylene, polyethylene, polystyrene, polycarbonate, polysulfone, polyetheretherketone, polyacrylonitrile, polyimide and polyphenylene oxide open-celled or closed-celled metal foams; open-celled or closed-celled polymeric foams; silica; porous glass; The porous support 7 may be a combination of two or more of these.

The porous support 7 has an average pore size of, for example, 0.01-0.4 μm. The thickness of the porous support 7 is not particularly limited, and is, for example, 10 μm or more, preferably 20 μm or more, and more preferably 50 μm or more. The thickness of the porous support 7 is, for example, 300 μm or less, preferably 200 μm or less, more preferably 150 μm or less.

<<Method for producing the first separation membrane>>
The first separation membrane 11 can be produced, for example, by the following method. First, a coating liquid containing the material for the intermediate layer 6 is prepared. Next, a coating liquid containing the material of the intermediate layer 6 is applied onto the porous support 7 to form a coating film. A method for applying the coating liquid is not particularly limited, and a wire bar or the like can be used, for example. The thickness of the intermediate layer 6 to be formed can be adjusted by adjusting the wire diameter of the wire bar and the concentration of the material of the intermediate layer 6 in the coating liquid. Alternatively, the coating film may be formed by immersing the porous support 7 in the coating liquid. Next, the coating film is dried to form the intermediate layer 6 . The coating film can be dried, for example, under heating conditions. The heating temperature of the coating film is, for example, 50° C. or higher. The heating time of the coating film is, for example, 1 minute or longer, and may be 5 minutes or longer.

The surface of the intermediate layer 6 can be subjected to an easy-adhesion treatment as necessary. Surface treatments such as application of a primer, corona discharge treatment, plasma treatment, etc. may be applied as the adhesion-promoting treatment.

Next, a coating liquid containing the material for the separation functional layer 5 is prepared. A coating liquid containing the material of the separation functional layer 5 is applied onto the intermediate layer 6 to obtain a coating film. This coating film is dried to form the separation functional layer 5 . As for the coating method and drying conditions of the coating liquid, the methods and conditions described above for the intermediate layer 6 can be used. The coating liquid containing the material of the separation functional layer 5 may be applied by spin coating. Thereby, the first separation membrane 11 is obtained.

The method of manufacturing the first separation membrane 11 is not limited to the above method. For example, the first separation membrane 11 can also be produced by the following method. For example, a coating liquid containing the material of the separation functional layer 5 is applied onto the transfer film to obtain a coating film. The separation functional layer 5 is formed by drying the coating film. Next, the intermediate layer 6 is formed by applying a coating liquid containing the material of the intermediate layer 6 onto the separation functional layer 5 and drying it. A laminate of the intermediate layer 6 and the separation functional layer 5 is transferred to the porous support 7 . Thereby, the first separation membrane 11 is obtained.

<<Characteristics of the first separation membrane>>
The permeation rate of carbon dioxide permeating through the first separation membrane 11 is not particularly limited. As an example, the permeation rate T _CO2 of carbon dioxide permeating the first separation membrane 11 is, for example, 5 GPU or more, preferably 10 GPU or more, more preferably 50 GPU or more, and still more preferably 100 GPU or more. The upper limit of the permeation rate T _CO2 is not particularly limited, and is, for example, 500 GPU.

The permeation rate T _CO2 can be calculated by the following method. First, a mixed gas containing carbon dioxide and hydrogen is supplied to a space adjacent to one surface of the first separation membrane 11 (for example, the main surface 11a of the first separation membrane 11 on the separation functional layer side), and the first separation is performed. A space adjacent to the other surface of the membrane 11 (for example, the main surface 11b of the first separation membrane 11 on the porous support side) is decompressed. Thereby, in the space adjacent to the other surface of the first separation membrane 11, the permeated gas that has passed through the first separation membrane 11 is obtained. The composition of the permeated gas, the weight of the permeated gas, etc. are measured. The permeation rate T _CO2 can be calculated from the measurement results. In the above operation, the concentration of carbon dioxide in the mixed gas is 50 vol% under standard conditions (0°C, 101 kPa). The mixed gas supplied to the space adjacent to one surface of the first separation membrane 11 has a temperature of 30° C. and a pressure of 0.1 MPa. The space adjacent to the other surface of the first separation membrane 11 is decompressed so that the pressure in the space is 0.1 MPa lower than the atmospheric pressure in the measurement environment.

Under the conditions for measuring the permeation rate T _CO2 , the separation coefficient α _CO2 of carbon dioxide with respect to hydrogen of the first separation membrane 11 is, for example, 20 or more, preferably 30 or more, more preferably 40 or more, and further Preferably it is 50 or more. The upper limit of the separation factor α _CO2 is not particularly limited, and is 100, for example. The separation factor α _CO2 can be calculated from the following formula. However, in the following formula, X _A and X _B are the volume ratio of carbon dioxide and the volume ratio of hydrogen in the mixed gas, respectively. Y _A and Y _B are the volume ratio of carbon dioxide and the volume ratio of hydrogen, respectively, in the permeated gas that has passed through the first separation membrane 11 .
Separation factor α _CO2 = (Y _A /Y _B )/(X _A /X _B )

[Second separation membrane unit]
As shown in FIG. 4 , the second separation membrane unit 20 includes a second separation membrane 21 and a tank 22 . Tank 22 has a third chamber 23 and a fourth chamber 24 . The space within the third chamber 23 corresponds to the supply side space, and the space within the fourth chamber 24 corresponds to the permeation side space. The second separation membrane 21 is arranged inside the tank 22 . Inside the tank 22 , the second separation membrane 21 separates the third chamber 23 and the fourth chamber 24 . The second separation membrane 21 extends from one of the pair of wall surfaces of the tank 22 to the other.

The third chamber 23 has an entrance 23a and an exit 23b. The fourth chamber 24 has an outlet 24a. An inlet 23 a of the third chamber 23 is an opening for supplying the first non-permeating gas 81 to the second separation membrane unit 20 . The outlet 24 a of the fourth chamber 24 is an opening for discharging the second permeable gas 90 obtained by the permeation of the first non-permeable gas 81 through the second separation membrane 21 from the second separation membrane unit 20 . The outlet 23 b of the third chamber 23 is an opening for discharging the first non-permeable gas 81 (second non-permeable gas 91 ) that has not permeated the second separation membrane 21 from the second separation membrane unit 20 . Each of the inlet 23a, the outlet 23b, and the outlet 24a is formed in the wall surface of the tank 22, for example.

(Second separation membrane)
The second separation membrane 21 can preferentially permeate the gas B contained in the first non-permeable gas 81 . As the second separation membrane 21 when the gas B is carbon dioxide, that is, the second separation membrane 21 that preferentially permeates carbon dioxide, the carbon dioxide permeable membrane described above for the first separation membrane 11 can be used. As the second separation membrane 21 when the gas B is hydrogen, that is, the second separation membrane 21 that preferentially permeates hydrogen, the hydrogen-permeable membrane described above for the first separation membrane 11 can be used.

In the gas separation system 100 of this embodiment, when the first separation membrane 11 is a hydrogen permeation membrane, the second separation membrane 21 is, for example, a carbon dioxide permeation membrane. When the first separation membrane 11 is a carbon dioxide permeation membrane, the second separation membrane 21 is, for example, a hydrogen permeation membrane. In other words, either one of the first separation membrane 11 and the second separation membrane 21 may be a hydrogen-permeable membrane and include a metal layer containing metal. Either one of the first separation membrane 11 and the second separation membrane 21 is a carbon dioxide permeable membrane and may have a separation functional layer containing a polyether block amide resin or an ionic liquid.

The first separation membrane unit 10 and the second separation membrane unit 20 included in the gas separation system 100 are suitable for a flow-through (continuous) membrane separation method. However, these separation membrane units may also be used for batch-type membrane separation methods.

[Mixed gas separation method]
In this embodiment, the method for separating the mixed gas 70 includes a first separation step using the first separation membrane 11, a second separation step using the second separation membrane 21, and a recovery step of recovering the second permeable gas 90 and the second non-permeable gas 91, respectively.

For example, the first separation step is performed as follows. First, the mixed gas 70 is supplied to the first chamber 13 (supply side space) of the first separation membrane unit 10 through the mixed gas supply path 30 . The mixed gas 70 is pressurized by, for example, the pressurizing device 40 and supplied to the first chamber 13 . The pressure of the mixed gas 70 pressurized by the pressurizing device 40, that is, the pressure in the supply-side space of the first separation membrane unit 10 is, for example, 0.1 MPa or more, preferably 0.5 MPa or more. It may be 0 MPa or more. The upper limit of the pressure of the mixed gas 70 is not particularly limited, and is, for example, 10.0 MPa. In this specification, unless otherwise specified, "pressure" means absolute pressure.

Mixed gas 70 includes Gas A and Gas B, as described above. As an example, (i) gas A is hydrogen and gas B is carbon dioxide, or (ii) gas A is carbon dioxide and gas B is hydrogen. Mixed gas 70 is typically an exhaust gas from a chemical plant, such as an exhaust gas produced by a shift reaction. However, the gas separation system 100 of this embodiment can also be used to separate mixed gases 70 having compositions other than those described above. For example, gas A or gas B may be one type of gas selected from nonpolar gases such as nitrogen, methane, and oxygen, inert gases such as helium, and acidic gases other than carbon dioxide. Examples of acid gases other than carbon dioxide include hydrogen sulfide, carbonyl sulfide, sulfur oxides (SO _x ), hydrogen cyanide, nitrogen oxides (NO _x ), and the like.

The content of gas A in the mixed gas 70 is, for example, 10 vol% or more, may be 25 vol% or more, may be 40 vol% or more, or may be 50 vol% or more. The upper limit of the content of gas A in mixed gas 70 is not particularly limited, and is, for example, 75 vol %. The content of the gas B in the mixed gas 70 is, for example, 10 vol% or more, may be 25 vol% or more, may be 40 vol% or more, or may be 50 vol% or more. The upper limit of the content of gas B in mixed gas 70 is not particularly limited, and is, for example, 75 vol %. In the mixed gas 70, the ratio of the volume of gas A to the total value of the volumes of gas A and gas B is not particularly limited, and is, for example, 25 to 75 vol%. In this specification, unless otherwise specified, "content" and "volume" mean values under standard conditions (0°C, 101 kPa).

The mixed gas 70 supplied to the first chamber 13 of the first separation membrane unit 10 is separated by the first separation membrane 11 . Thereby, the first permeating gas 80 is supplied to the second chamber 14 . The first permeable gas 80 supplied to the second chamber 14 is discharged to the outside of the first separation membrane unit 10 through the outlet 14a. The first permeating gas 80 is discharged from the discharge port 42 through the discharge path 34 .

As described above, the first separation membrane 11 of the first separation membrane unit 10 preferentially permeates the gas A contained in the mixed gas 70 . Therefore, the first permeable gas 80 obtained in the first separation membrane unit 10 has a higher content of gas A than the mixed gas 70 . The content of gas A in the first permeable gas 80 is not particularly limited, and is, for example, 50 to 99 vol %. The ratio of the gas A content (vol %) in the first permeable gas 80 to the gas A content (vol %) in the mixed gas 70 is not particularly limited, and is, for example, 2-9.

In the gas separation system 100, the membrane area of the first separation membrane 11 is set smaller than that of the second separation membrane 21. Therefore, the volume of the first permeable gas 80 processed by the first separation membrane 11 tends to be relatively small. As an example, the ratio of the volume of the first permeable gas 80 separated by the first separation membrane 11 to the volume of the mixed gas 70 supplied to the first separation membrane unit 10 is not particularly limited. 50 vol %. In the above ratio, the volumes of the mixed gas 70 and the first permeable gas 80 are values under standard conditions (0° C., 101 kPa).

The concentration of the gas B in the mixed gas 70 gradually increases from the inlet 13a of the first chamber 13 toward the outlet 13b. The content of gas B in the mixed gas 70 (first non-permeable gas 81) processed in the first chamber 13 is not particularly limited, and is, for example, 25 to 75 vol%. The first non-permeable gas 81 is discharged to the outside of the first separation membrane unit 10 through the outlet 13b. The first non-permeable gas 81 is supplied to the second separation membrane unit 20 through the non-permeable gas supply path 32 .

For example, the second separation process is performed as follows. First, the first non-permeable gas 81 is supplied to the third chamber 23 (supply side space) of the second separation membrane unit 20 through the non-permeable gas supply path 32 . The first non-permeating gas 81 has, for example, the same pressure as the mixed gas 70 supplied to the first separation membrane unit 10 . The pressure of the first non-permeating gas 81, that is, the pressure in the supply-side space of the second separation membrane unit 20 is, for example, 0.1 MPa or more, preferably 0.5 MPa or more, or 1.0 MPa or more. good too. The upper limit of the pressure of the first non-permeable gas 81 is not particularly limited, and is, for example, 10.0 MPa.

The first non-permeable gas 81 supplied to the third chamber 23 of the second separation membrane unit 20 is separated by the second separation membrane 21 . Thereby, the second permeating gas 90 is supplied to the fourth chamber 24 . The second permeating gas 90 supplied to the fourth chamber 24 is discharged to the outside of the second separation membrane unit 20 through the outlet 24a. The second permeating gas 90 is sent to the first recovery section 44 through the first recovery path 36 .

As described above, the second separation membrane 21 of the second separation membrane unit 20 preferentially permeates the gas B contained in the first non-permeable gas 81 . Therefore, the second permeable gas 90 obtained by the second separation membrane unit 20 has a higher gas B content than the first non-permeable gas 81 . The content of the gas B in the second permeable gas 90 is not particularly limited, and is, for example, 70 vol% or more, preferably 80 vol% or more, more preferably 90 vol% or more, and still more preferably 95 vol% or more. . In particular, when the composition of the mixed gas 70 is gas A/gas B=50/50 in volume ratio, the content of gas B in the second permeable gas 90 is preferably 70 vol % or more. The ratio of the gas B content (vol %) in the second permeable gas 90 to the gas B content (vol %) in the first non-permeable gas 81 is not particularly limited, and is, for example, 2-9.

The volume ratio of the second permeable gas 90 separated by the second separation membrane 21 to the volume of the first non-permeable gas 81 supplied to the second separation membrane unit 20 is not particularly limited, and is, for example, 50 to 95 vol%. is. The above ratio may be 2.5-50 vol %. In the above ratio, the volumes of the first non-permeable gas 81 and the second permeable gas 90 are values under standard conditions (0° C., 101 kPa).

The concentration of gas A in the first non-permeating gas 81 gradually increases from the inlet 23a of the third chamber 23 toward the outlet 23b. The content of the gas A in the first non-permeable gas 81 (second non-permeable gas 91) processed in the third chamber 23 is not particularly limited, and is, for example, 70 vol% or more, preferably 80 vol% or more, More preferably 90 vol% or more, still more preferably 95 vol% or more. In particular, when the composition of the mixed gas 70 is gas A/gas B=50/50 in volume ratio, the content of gas A in the second impermeable gas 91 is preferably 70 vol % or more. The second non-permeable gas 91 is discharged to the outside of the second separation membrane unit 20 through the outlet 23b. The second non-permeating gas 91 is sent to the second recovery section 46 through the second recovery path 38 .

In the separation method of this embodiment, the first separation step and the second separation step are, for example, continuously performed. That is, the first non-permeating gas 81 separated in the first separation step is immediately supplied to the second separation step without being collected in a tank or the like. By continuously performing the first separation process and the second separation process, the throughput of the mixed gas 70 per unit time can be easily increased.

In the recovery step, the second permeation gas 90 in which the gas B is concentrated is recovered by the first recovery unit 44 . The second recovery unit 46 recovers the second non-permeating gas 91 in which the gas A is concentrated. The recovery rate of the gas B by the second permeable gas 90 is not particularly limited, and is, for example, 70% or more, preferably 80% or more, more preferably 90% or more, and still more preferably 95% or more. . The recovery rate of the gas A by the second non-permeating gas 91 is not particularly limited, and is, for example, 60% or more, preferably 70% or more, more preferably 80% or more, and still more preferably 90% or more. be. As used herein, the recovery rate means the ratio of the weight of the recovered gas to the weight of the specific gas contained in the mixed gas. In addition, "weight" means the value in a standard state (0 degreeC, 101 kPa).

In conventional gas separation systems, the membrane area of the first separation membrane is usually set to be approximately the same as the membrane area of the second separation membrane, and the first permeated gas that has permeated the first separation membrane and the second separation The second permeated gas that has permeated the membrane is recovered. According to studies by the present inventors, in this method, in order to improve the recovery rates of gas A and gas B, it is necessary to greatly increase the membrane areas of the first separation membrane and the second separation membrane. However, when the membrane area of these separation membranes increases, not only does the manufacturing cost increase, but the content of gas A in the first permeable gas and the content of gas B in the second permeable gas tend to decrease.

On the other hand, in the gas separation system 100 of the present embodiment, the membrane area of the first separation membrane 11 is set smaller than the membrane area of the second separation membrane 21, and furthermore, the second permeable gas 90 and the second non-permeable gas Gas 91 is recovered. According to this gas separation system 100, each of the gas A and the gas B can be separated with high purity and high purity without greatly increasing the total value of the membrane area of the first separation membrane 11 and the membrane area of the second separation membrane 21. It tends to be recoverable at a recovery rate. Thus, the gas separation system 100 of this embodiment is suitable for efficiently separating a mixed gas.

As described above, in the gas separation system 100 of the present embodiment, the membrane area M1 of the first separation membrane 11 and the membrane area M2 of the second separation membrane 21 satisfy the following relational expression (1). However, in the gas separation system 100, the following relational expression (2) or the following relational expression (3) may be satisfied instead of or together with the relational expression (1). In relational expression (2), T1 means the permeation rate of gas A passing through the first separation membrane 11 and T2 means the permeation rate of gas B passing through the second separation membrane 21 . In relational expression (3), α1 means the separation factor of gas A with respect to gas B of the first separation membrane 11 , and α2 means the separation factor of gas B with respect to gas A of the second separation membrane 21 . The permeation rates T1 and T2 and the separation factors α1 and α2 can be measured by the same method as described above for the hydrogen permeable membrane, except that a mixed gas consisting of gas A and gas B is used.
M1<M2 (1)
M1×T1<M2×T2 (2)
M1×α1<M2×α2 (3)

[Modified Example of First Separation Membrane Unit]
In the gas separation system 100, the first separation membrane unit 10 may be a spiral membrane element as shown in FIG. The first separation membrane unit 15 of FIG. 5 has a central tube 16 and a laminate 17 . A laminate 17 includes a first separation membrane 11 .

The central tube 16 has a cylindrical shape. A plurality of holes or slits are formed on the surface of the central tube 16 to allow the first permeating gas 80 to flow into the central tube 16 . Examples of materials for the central tube 16 include resins such as acrylonitrile-butadiene-styrene copolymer resin (ABS resin), polyphenylene ether resin (PPE resin), and polysulfone resin (PSF resin); and metals such as stainless steel and titanium. be done. The inner diameter of the central tube 16 is, for example, in the range of 20-100 mm.

In addition to the first separation membrane 11, the laminate 17 further includes a feed-side channel material 18 and a permeate-side channel material 19. Laminate 17 is wound around central tube 16 . The first separation membrane unit 15 may further include an exterior material (not shown).

As the feed side channel material 18 and the permeate side channel material 19, for example, a resin made of polyethylene, polypropylene, polyethylene terephthalate (PET), polyphenylene sulfide (PPS) or ethylene-chlorotrifluoroethylene copolymer (ECTFE) is used. Net, woven or knitted fabrics can be used.

Membrane separation using the first separation membrane unit 15 is performed, for example, by the following method. First, the mixed gas 70 is supplied to one end of the wound laminate 17 . As a result, the first permeating gas 80 that has permeated the first separation membrane 11 of the laminate 17 moves into the central tube 16 . The first permeating gas 80 is discharged outside through the central tube 16 . The mixed gas 70 (first non-permeable gas 81 ) processed by the first separation membrane unit 15 is discharged outside from the other end of the wound laminate 17 .

In the gas separation system 100, the second separation membrane unit 20 may be a spiral membrane element having the same configuration as the first separation membrane unit 15.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these.

(Calculation example 1)
A simulation of the operation of the gas separation system shown in FIG. 1 was performed using the process modeling software Symmetry manufactured by Schlumberger. Specifically, the gas separation system shown in FIG. 1 uses a hydrogen permeable membrane as the first separation membrane, uses a carbon dioxide permeable membrane as the second separation membrane, was assumed to be collected. A gas separation system for this assumption is sometimes referred to as Model 1-1. For the hydrogen permeable membrane, the hydrogen permeation rate T _H2 was set to 100 GPU, and the separation factor α _H2 of hydrogen with respect to carbon dioxide was set to 50. Similarly, for the carbon dioxide permeable membrane, the permeation rate of carbon dioxide T _CO2 was set to 100 GPU, and the separation coefficient α _CO2 of carbon dioxide to hydrogen was set to 50. Further, the mixed gas supply conditions and the carbon dioxide recovery conditions were set as follows. It is assumed that the mixed gas is pressurized from the atmospheric pressure (101.33 kPa) in the external environment to 1 MPa by a pressurizing device arranged in the mixed gas supply path.
[Conditions of supply of mixed gas]
Flow rate: 1016.47 Nm ³ /hr
Composition (volume ratio): _CO2 / _H2 = 50/50
_CO2 weight: 1000kg/hr
_H2 weight: 45.81 kg/hr
Pressure: 1MPa
Temperature: 25°C
[Conditions for collecting carbon dioxide]
Purity (CO ₂ content in second permeate gas): 95 vol%
Recovery rate (ratio of _CO2 weight in second permeate gas to _CO2 weight in mixed gas): 80%

By the simulation of Calculation Example 1, the membrane area of the separation membrane required to separate the mixed gas using the gas separation system, the purity of hydrogen ( _H2 content in the second non-permeating gas), and the recovery rate of hydrogen (the ratio of _H2 weight in the second impermeant gas to _H2 weight in the mixed gas) was calculated. Table 1 shows the results.

(Calculation example 2)
A simulation of Calculation Example 2 was performed in the same manner as in Calculation Example 1, except that the first permeation gas and the second permeation gas were assumed to be recovered. The gas separation system for the assumptions of Calculation Example 2 is sometimes referred to as Model 1-2. By the simulation of Calculation Example 2, the membrane area of the separation membrane required to separate the mixed gas using the gas separation system, the purity of hydrogen ( _H2 content in the first permeated gas), and the recovery rate of hydrogen ( The ratio of _H2 weight in the first permeate gas to _H2 weight in the mixed gas) was calculated. Table 1 shows the results.

(Calculation example 3)
Using process modeling software Symmetry manufactured by Schlumberger, a simulation was performed when the gas separation system 200 shown in FIG. 6 was operated. The gas separation system 200 includes a first separation membrane unit 210 containing a first separation membrane 211 and a second separation membrane unit 220 containing a second separation membrane 221 . The first separation membrane 211 and the second separation membrane 221 respectively correspond to the first separation membrane 11 and the second separation membrane 21 of the gas separation system 100 of FIG. However, the second separation membrane 221 is configured to separate the first permeable gas that has permeated the first separation membrane 211 into a second permeable gas and a second non-permeable gas.

The gas separation system 200 includes a mixed gas supply route 230 , a first recovery route 232 , a permeated gas supply route 234 , an exhaust route 236 and a second recovery route 238 . The mixed gas supply route 230 is a route for supplying the mixed gas to the first separation membrane unit 210 . A pressure device 240 for pressurizing the mixed gas is arranged in the mixed gas supply path 230 .

The first recovery path 232 is connected to the non-permeable gas outlet of the first separation membrane unit 210 and is a path for recovering the first non-permeable gas from the first separation membrane unit 210 .

The permeated gas supply path 234 is connected to the permeated gas outlet of the first separation membrane unit 210 and the permeated gas inlet of the second separation membrane unit 220 to supply the first permeated gas from the first separation membrane unit 210 to the second separation membrane unit 220. is a route for supplying A pressurizing device 242 for increasing the pressure of the first permeating gas is arranged in the permeating gas supply path 234 .

The discharge path 236 is connected to the permeated gas outlet of the second separation membrane unit 220 and is a path for discharging the second permeated gas from the second separation membrane unit 220 . The second recovery path 238 is connected to the non-permeating gas outlet of the second separation membrane unit 220 and is a path for recovering the second non-permeating gas from the second separation membrane unit 220 .

Calculation Example 3 uses a carbon dioxide permeable membrane as the first separation membrane 211, uses a hydrogen permeable membrane as the second separation membrane 221, and recovers the first non-permeable gas and the second non-permeable gas. assumed. A gas separation system for this assumption is sometimes referred to as Model 2. A simulation of Calculation Example 3 was performed in the same manner as in Calculation Example 1, except that Model 2 was used. Incidentally, in the gas separation system 200, the pressure of the first permeated gas that permeates the first separation membrane 211 usually matches the atmospheric pressure in the external environment. Therefore, in Calculation Example 3, it was assumed that the pressure of the first permeating gas was increased to 1 MPa by the pressurizing device 242 arranged in the permeating gas supply path 234 . That is, in Calculation Example 3, it was assumed that the pressurization device 240 pressurized the mixed gas and the pressurization device 242 pressurized the first permeated gas.

By the simulation of Calculation Example 3, the membrane area of the separation membrane required for separating the mixed gas using the gas separation system, the purity of hydrogen ( _H2 content in the first non-permeating gas), and the recovery rate of hydrogen (Ratio of _H2 weight in the first impermeant gas to _H2 weight in the mixed gas) was calculated. Table 1 shows the results.

(Calculation example 4)
The simulation of Calculation Example 4 was performed in the same manner as in Calculation Example 1, except that a carbon dioxide permeable membrane was used as the first separation membrane and a hydrogen permeable membrane was used as the second separation membrane. The gas separation system for the assumptions of Calculation Example 4 is sometimes referred to as Model 3-1. By the simulation of Calculation Example 4, the membrane area of the separation membrane required to separate the mixed gas using the gas separation system, the purity of hydrogen ( _H2 content in the second permeated gas), and the recovery rate of hydrogen ( The ratio of _H2 weight in the second permeate gas to _H2 weight in the mixed gas) was calculated. Table 1 shows the results.

(Calculation example 5)
The simulation of Calculation Example 5 was performed in the same manner as in Calculation Example 4, except that the first permeation gas and the second permeation gas were assumed to be recovered. The gas separation system for the assumptions of Calculation Example 5 is sometimes referred to as Model 3-2. In the simulation of Calculation Example 5, the carbon dioxide recovery conditions described above could not be achieved. Therefore, the membrane area of the first separation membrane was set to 840 m ² and the membrane area of the second separation membrane was set to 463 m ² . Carbon dioxide purity ( _CO2 content in the first permeate gas), carbon dioxide recovery (ratio of _CO2 weight in the first permeate gas to _CO2 weight in the mixed gas), hydrogen purity ( The _H2 content in the second permeate gas) and the recovery rate of hydrogen (the ratio of the _H2 weight in the second permeate gas to the _H2 weight in the mixed gas) were calculated. Table 1 shows the results.

(Calculation example 6)
Using the process modeling software Symmetry manufactured by Schlumberger, a simulation was performed when the gas separation system 300 shown in FIG. 7 was operated. A gas separation system 300 includes a separation membrane unit 310 containing a separation membrane 311 . The separation membrane 311 corresponds to the first separation membrane 11 of the gas separation system 100 of FIG. Gas separation system 300 has the same configuration as gas separation system 100 in FIG. 1 except that it does not include a second separation membrane unit.

The gas separation system 300 includes a mixed gas supply path 330 , a first recovery path 332 and a second recovery path 334 . Mixed gas supply path 330 is a path for supplying mixed gas to separation membrane unit 310 . A pressure device 340 for pressurizing the mixed gas is arranged in the mixed gas supply path 330 .

The first recovery path 332 is connected to the permeation gas outlet of the separation membrane unit 310 and is a path for recovering the permeation gas from the separation membrane unit 310 . The second recovery path 334 is connected to the non-permeating gas outlet of the separation membrane unit 310 and is a path for recovering the non-permeating gas from the separation membrane unit 310 .

In Calculation Example 6, it is assumed that a hydrogen permeable membrane is used as the separation membrane and that the permeable gas and the non-permeable gas are recovered. A gas separation system for this assumption is sometimes referred to as Model 4. A simulation of Calculation Example 6 was performed in the same manner as in Calculation Example 1, except that Model 4 was used. By the simulation of Calculation Example 6, the membrane area of the separation membrane required to separate the mixed gas using the gas separation system, the purity of hydrogen (H ₂ content in the permeated gas), and the recovery rate of hydrogen (mixed gas The ratio of the _H2 weight in the permeate gas to the _H2 weight in the permeate gas) was calculated. Table 1 shows the results.

(Calculation example 7)
Regarding the gas separation system 200 shown in FIG. A simulation of Calculation Example 7 was performed in the same manner as in Calculation Example 3, except that the collection of was assumed. The gas separation system for the assumptions of Example 7 is sometimes referred to as Model 5. By the simulation of Calculation Example 7, the membrane area of the separation membrane required to separate the mixed gas using the gas separation system, the purity of hydrogen ( _H2 content in the first non-permeating gas), and the recovery rate of hydrogen (Ratio of _H2 weight in the first impermeant gas to _H2 weight in the mixed gas) was calculated. Table 1 shows the results.

As can be seen from Table 1, in Calculation Examples 1 and 4 using the gas separation system of the present embodiment, without significantly increasing the total value of the membrane area of the first separation membrane and the membrane area of the second separation membrane, Carbon dioxide and hydrogen could be recovered with high purity and high yield. Thus, according to the gas separation system of this embodiment, the mixed gas can be efficiently separated.

In particular, from the results of Calculation Examples 1, 4 and 6, in the gas separation system of this embodiment, by combining two types of separation membranes, compared to a gas separation system equipped with one type of separation membrane, the required membrane It can be seen that the area can be greatly reduced.

(Calculation examples 8 to 12)
In Calculation Examples 8 to 12, similar to Calculation Example 1, simulations were performed when the model 1-1 was operated. In Calculation Examples 8 to 12, the ratio of the membrane area of the first separation membrane to the membrane area of the second separation membrane was changed from the conditions of Calculation Example 1, and the influence thereof was confirmed. Table 2 shows the results.

As can be seen from Table 2, in calculation examples 1 and 8 to 10 in which the membrane area of the first separation membrane is smaller than the membrane area of the second separation membrane, carbon dioxide and hydrogen are each recovered at high purity and high recovery rate. was made. In Calculation Examples 1, 8, and 9, in which the ratio of the membrane area of the first separation membrane to the membrane area of the second separation membrane is 10/90 or less, the purity and recovery rate of carbon dioxide and hydrogen were particularly high. .

(Calculation examples 13 to 17)
In Calculation Examples 13 to 17, similar to Calculation Example 2, simulations were performed when the model 1-2 was operated. In Calculation Examples 13 to 17, the ratio of the membrane area of the first separation membrane to the membrane area of the second separation membrane was changed from the conditions of Calculation Example 2, and the influence thereof was confirmed. Table 3 shows the results.

As can be seen from Table 3, in model 1-2 in which the first permeation gas and the second permeation gas are recovered, even if the membrane areas of the first separation membrane and the second separation membrane are adjusted, each of carbon dioxide and hydrogen is high. It was difficult to recover the recovery rate.

(Calculation examples 18-21)
In Calculation Examples 18 to 21, similar to Calculation Example 4, simulations were performed when the model 3-1 was operated. In Calculation Examples 18 to 21, the ratio of the membrane area of the first separation membrane to the membrane area of the second separation membrane was changed from the conditions of Calculation Example 4, and the influence thereof was confirmed. Table 4 shows the results.

As can be seen from Table 4, in Calculation Examples 4 and 18 to 19 in which the membrane area of the first separation membrane is smaller than the membrane area of the second separation membrane, carbon dioxide and hydrogen are each recovered with high purity and high recovery rate. was made.

(Calculation examples 22 to 28)
For the hydrogen permeable membrane, the hydrogen permeation rate T _H2 was set to 50 GPUs, and the separation factor α _H2 of hydrogen with respect to carbon dioxide was set to 40. For the carbon dioxide permeable membrane, the carbon dioxide permeation rate T _CO2 was set to 50 GPUs. Calculation Examples 22 to 28 were simulated in the same manner as in Calculation Examples 1 to 7, respectively, except that the separation factor α _CO2 of carbon dioxide with respect to hydrogen was set to 40. Table 5 shows the results. However, in the simulation of Calculation Example 26, the carbon dioxide recovery conditions described above for Calculation Example 1 could not be achieved, and appropriate calculation results could not be obtained.

As can be seen from Table 5, even when the separation performance of the hydrogen permeable membrane and the carbon dioxide permeable membrane is changed, in Calculation Examples 22 and 25 using the gas separation system of the present embodiment, the membrane area of the first separation membrane , and the membrane area of the second separation membrane did not increase significantly, and carbon dioxide and hydrogen could be recovered with high purity and high recovery rate.

(Calculation examples 29-31)
In Calculation Examples 29 and 31, the ratio of the membrane area of the first separation membrane to the membrane area of the second separation membrane was changed from the conditions of Calculation Examples 22, 23, and 25, respectively, and the influence thereof was confirmed. Table 6 shows the results.

As can be seen from Table 6, in Calculation Examples 22 and 25 using the gas separation system of the present embodiment in which the membrane area of the first separation membrane is smaller than the membrane area of the second separation membrane, each of carbon dioxide and hydrogen has a high purity. And it was possible to recover with a high recovery rate.

The gas separation system of this embodiment is suitable for separating a mixed gas, such as a mixed gas containing carbon dioxide and hydrogen. In particular, the gas separation system of the present embodiment is suitable for processing off-gases from chemical plants.

Claims (12)

a first separation membrane that separates the mixed gas into a first permeable gas and a first non-permeable gas;
a second separation membrane that separates the first non-permeable gas into a second non-permeable gas and a second non-permeable gas;
with
The mixed gas includes a gas A and a gas B different from the gas A,
The first separation membrane can preferentially permeate the gas A,
The second separation membrane can preferentially permeate the gas B,
the membrane area of the first separation membrane is smaller than the membrane area of the second separation membrane,
A gas separation system for recovering the second permeate gas and the second non-permeate gas, respectively. The gas separation system according to claim 1, wherein the ratio of said membrane area of said first separation membrane to said membrane area of said second separation membrane is 10/90 or less. Claim 1 wherein (i) said gas A is hydrogen and said gas B is carbon dioxide, or (ii) said gas A is carbon dioxide and said gas B is hydrogen. A gas separation system as described in . The content of the gas B in the second permeable gas is 70 vol% or more,
The gas separation system according to claim 1, wherein the content of said gas A in said second non-permeable gas is 70 vol% or more. The recovery rate of the gas B by the second permeable gas is 70% or more,
2. The gas separation system according to claim 1, wherein the recovery rate of said gas A with said second non-permeating gas is 60% or more. The gas separation system according to claim 1, wherein in the mixed gas, the ratio of the volume of the gas A to the total value of the volume of the gas A and the volume of the gas B is 25 to 75 vol%. a first separation membrane unit containing the first separation membrane;
a mixed gas supply path connected to the first separation membrane unit for supplying the mixed gas to the first separation membrane unit;
a pressurizing device arranged in the mixed gas supply path for pressurizing the mixed gas;
2. The gas separation system of claim 1, further comprising: a second separation membrane unit containing the second separation membrane;
a first collection unit that collects the second permeation gas;
a first recovery path connected to the second separation membrane unit and the first recovery section for sending the second permeated gas to the first recovery section;
2. The gas separation system of claim 1, further comprising: a second separation membrane unit containing the second separation membrane;
a second collection unit that collects the second non-permeable gas;
a second recovery path connected to the second separation membrane unit and the second recovery section for sending the second non-permeable gas to the second recovery section;
2. The gas separation system of claim 1, further comprising: The gas separation system according to claim 1, wherein one of the first separation membrane and the second separation membrane comprises a metal layer containing metal. 　The gas separation system according to claim 1, wherein one of the first separation membrane and the second separation membrane comprises a separation functional layer containing a polyether block amide resin or an ionic liquid. A mixed gas containing the gas A and a gas B different from the gas A is separated into a first permeable gas and a first non-permeable gas by a first separation membrane capable of preferentially permeating the gas A. a first separation step;
a second separation step of separating the first non-permeable gas into a second non-permeable gas and a second non-permeable gas by a second separation membrane capable of preferentially permeating the gas B;
a recovery step of recovering the second permeable gas and the second non-permeable gas, respectively;
including
A method for separating a mixed gas, wherein the membrane area of the first separation membrane is smaller than the membrane area of the second separation membrane.

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